Meeting the ever increasing fresh water needs of the growing world population is one of the most serious global challenges of the 21st century. Apart from the improved use of existing fresh water resources, desalination and water reuse are considered to be critical to overcome water scarcity that is affecting roughly half of the world's population. Two methods, namely, thermal desalination and reverse osmosis technology have been widely employed for desalination of sea water, which represents a virtually unlimited source. Solar water desalination, which relies on a sustainable and renewable energy source, is a promising method to alleviate fresh water scarcity in parts of the world with ample sunlight with low environmental impact. Steam generation using solar energy has been proven to be technically feasible and considered to be highly promising for water purification using sustainable energy source. However, low efficiency due to the heat loss associated with heating the bulk water and the requirement for high optical concentration limit the utilization of solar desalination in stand-alone solar power applications.
Previous designs involve either expensive materials or complex fabrication methods, with poor prospects in terms of scalability. Thus, there is a need for cost-effective and scalable heat-localization layers that provide high steam-generation efficiency. Additionally, most of these materials have a finite lifetime owing to pore clogging, degradation of the photothermal properties, and alteration of the surface properties of the water transport layer. Disposal of these materials can quickly pose a significant threat to the environment and ecosystems. For example, degradation and leaching of nanoscale photothermal materials into marine ecosystems, where these materials are most likely deployed can have lasting negative consequences. Thus, there is a need for a biodegradable composition for solar steam generation that provides high steam generation efficiency.